Non-perfluoro fluorine-containing resin molded article having low-temperature heat-sealing property

ABSTRACT

An excellent low temperature heat sealing property is imparted to a surface of a non-perfluoro fluorine-containing resin molded article having F/C of not more than 1.8. A non-perfluoro fluorine-containing resin molded article having a surface layer portion having a low temperature heat sealing property on at least a part of the surface layer thereof; said surface layer portion having a low temperature heat-sealing property has a ratio F/C of the number of fluorine atoms to the number of carbon atoms of 0.2≦F/C≦0.9 and a ratio O/C of the number of oxygen atoms to the number of carbon atoms of 0.09≦O/C≦0.40, and a remaining portion of the surface layer has a ratio F/C of the number of fluorine atoms to the number of carbon atoms which is larger than that of the surface layer portion having a low temperature heat-sealing property and is 0.8≦F/C≦1.8.

TECHNICAL FIELD

The present invention relates to a non-perfluoro fluorine-containingresin molded article having a heat-sealing property at low temperatureand a high adhesive strength, particularly to a cover film for solarbatteries.

BACKGROUND ART

Since fluorine-containing resins have excellent non-sticking property,fluorine-containing resin molded articles cannot be jointed with eachother or with a different material only by using an adhesive.

Also for joining the fluorine-containing resin molded articles with eachother, high frequency welding and ultrasonic wave welding which areusually used in processing general-purpose resins cannot be employedbecause parts to be jointed cannot be melted again. Accordingly withrespect to heat-meltable fluorine-containing resins, so-called meltadhesion method, in which the resin is subjected to heating at atemperature of not less than a melting point thereof and then pressingin a re-molten state, has been used. However in the melt adhesionmethod, since the fluorine-containing resin molded article is oncemelted, a mechanical strength thereof around a jointed part is loweredremarkably.

On the other hand, when the fluorine-containing resin molded article isjointed with a different kind of material, there is a chemicallytreating method, in which a surface of the fluorine-containing resinmolded article is chemically modified with sodium-naphthalene and thenjoining is carried out by using an adhesive. However the method has aproblem with coloring of the molded article and therefore cannot be usedfor applications where transparency is required.

To solve the above-mentioned problems, there are various proposals fordischarge-treatment of a surface of the molded article.

For example, there are the following known methods.

(1) A method of low temperature plasma treatment by glow discharging ofa molded article of perfluoro fluorine-containing resin such aspolytetrafluoroethylene, tetrafluoroethylene/perfluoro(alkyl vinylether) copolymer ortetrafluoroethylene/hexafluoropropylene/perfluoro(alkyl vinyl ether)copolymer having a ratio of the number of fluorine atoms to the numberof carbon atoms (hereinafter referred to as “F/C”) of 1.8 to 2.0 todecrease F/C on the surface of molded article to 0.5 to 1.75 and thenheat-sealing at a temperature of about 210° C. without using an adhesive(JP-B-5-68496),

(2) A method of low temperature plasma treatment by glow discharging ofa molded article of perfluoro fluorine-containing resin having a ratioF/C of the number of fluorine atoms to the number of carbon atoms of 1.9to 2.0 in non-polymerizable gas atmosphere having an oxygen content ofnot more than 10% by mole to decrease F/C of the surface of moldedarticle to 0.8 to 1.8 and to adjust a ratio of the number of oxygenatoms to the number of carbon atoms (hereinafter referred to as “O/C”)to not more than (0.2-0.09×(F/C)) and then heat-sealing at a temperatureof about 210° C. without using an adhesive (JP-B-2-54848),

(3) A method of discharge treatment of a surface of molded article ofperfluoro fluorine-containing resin in a stream of an organic compoundhaving functional group (for example, ketone and acrylic acid monomer)to impart a heat-sealing property to the surface (JP-B-37-17485,JP-B-49-12900, U.S. Pat. No.3,296,011),

(4) A method of continuous plasma treatment of a surface of a sheet in achamber charged with helium gas or a gas mixture mainly comprisinghelium gas (JP-A-3-143930), or a method of imparting a hydrophilicproperty to plastic and fiber by glow discharging at atmosphericpressure in a stream with steam of a rare gas or gas mixture of rare gasand ketone (JP-A-6-182195),

(5) A method of modifying a surface of perfluoro or non-perfluorofluorine-containing resin molded article by discharge treatment such ascorona discharging, glow discharging and plasma discharging in an inertgas atmosphere containing an organic compound having functional group(for example, acetone, glycidyl methacrylate, methanol, or the like) andthen jointing by using an adhesive having functional group havingaffinity to a functional group of the organic compound (Japanese PatentNo.2690032), and the like method.

However the above-mentioned methods (1) to (3) are directed to onlyperfluoro fluorine-containing resin molded articles, and treatment underreduced pressure is required.

In the method (4), since the fluorine-containing resin film is passedbetween the parallel plate type electrodes, the both sides of the filmis treated, thus greatly lowering non-sticking property, waterrepellency, lubricity, stain-proofing property and chemical resistancewhich are features of the fluorine-containing resin. In order to makethe best use of such features of the fluorine-containing resin, anopposite side of the film which is not treated must be covered with aprotection film. Further in the method described in JP-A-6-182195, sincean inert gas or fluorocarbon is used, the treating system must be madeair-tight and collection of exhaust gas has to be considered.

The method (5) is featured by coating an adhesive having a functionalgroup having a specific relation to the organic compound used as anatmosphere.

As mentioned above, improvements have been made mainly in heat-sealingproperty of perfluoro fluorine-containing resin molded articles havingF/C exceeding 1.8. However a heat-sealing property of non-perfluorofluorine-containing resins having F/C of not more than 1.8 is notenhanced as compared with perfluoro fluorine-containing resins only incase of the same treatment as in perfluoro fluorine-containing resins,and in many cases, an adhesive is necessary.

An object of the present invention is to impart excellent lowtemperature heat-sealing property to a surface of molded article ofnon-perfluoro fluorine-containing resin having F/C of not more than 1.8.

DISCLOSURE OF INVENTION

The present invention relates to a non-perfluoro fluorine-containingresin molded article, particularly a molded article in the form of filmhaving a surface layer portion having a low temperature heat sealingproperty on at least a part of the surface layer thereof, in which aratio F/C of the surface layer portion having a low temperatureheat-sealing property is 0.2≦F/C≦0.9, preferably 0.3≦F/C≦0.8,particularly preferably 0.4≦F/C≦0.8 and a ratio O/C thereof is0.09≦O/C≦0.40, preferably 0.14≦O/C≦0.30, particularly preferably0.14≦O/C≦0.25, and a ratio F/C of the remaining portion of the surfacelayer is larger than that of the surface layer portion having a lowtemperature heat-sealing property and is 0.8≦F/C≦1.8.

The molded article in the form of film is suitable as a cover film forsolar batteries, in which one side of the film has a surface layerportion having a low temperature heat-sealing property and a highheat-sealing strength. The molded article can also be used as alaminated article for covering of solar batteries by heat-sealingdirectly to an ethylene/vinyl acetate film or sheet at a temperatureless than a melting point of the non-perfluoro fluorine-containingresin.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a graph showing a relation between F/C, O/C and heat-sealingstrength of ETFE film subjected to discharge treatment which weremeasured in Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples of the non-perfluoro fluorine-containing resin which is used inthe present invention and has F/C of 0.7 to 1.8 are, for instance,ethylene-tetrafluoroethylene copolymer (ETFE),ethylene-tetrafluoroethylene-hexafluoropropylene copolymer,polyvinylidene fluoride (PVdF), vinylidene fluoride-tetrafluoroethylenecopolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE),vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidenefluoride-tetrafluoroethylene-hexafluoropropylene copolymer (THV), andthe like. Particularly for the laminated film for covering of solarbatteries, ETFE is preferred from the viewpoint of high transparency,mechanical strength and stress crack resistance.

It is preferable that the molded article of non-perfluorofluorine-containing resin is in the form of film or sheet. The moldedarticle may be in various forms such as plate, pipe, fiber, cloth (wovenfabric, knitted fabric) and laminated article thereof.

With respect to the non-perfluoro fluorine-containing resin moldedarticle having F/C of from 0.7 to 1.8, F/C thereof can be reduced to 0.2to 0.9 and O/C can be adjusted to 0.09 to 0.40 by discharge treatment ofa surface of the molded article in an atmosphere of a mixture of inertgas and reactive organic compound.

Examples of the inert gas are, for instance, nitrogen gas, helium gas,argon gas, and the like.

The reactive organic compound is a polymerizable or non-polymerizableorganic compound having oxygen atom. Examples thereof are vinyl esterssuch as vinyl acetate and vinyl formate; acrylic acid esters such asglycidyl methacrylate; ethers such as vinyl ethyl ether, vinyl methylether and glycidyl methyl ether; carboxylic acids such as acetic acidand formic acid; alcohols such as methyl alcohol, ethyl alcohol, phenoland ethylene glycol; ketones such as acetone and methyl ethyl ketone;carboxylic acid esters such as ethyl acetate and ethyl formate; acrylicacids such as acrylic acid and methacrylic acid; and the like. From thepoint that an activity of the modified surface is difficult to be lost(life is long) and from the viewpoint of safety and easy handling, vinylesters, acrylic acid esters and ketones are preferable, and particularlyvinyl acetate and glycidyl methacrylate are preferable.

A concentration of the reactive organic compound varies depending onkinds of the organic compound and fluorine-containing resin and isusually from 0.1 to 3.0% by volume, preferably 0.1 to 1.0% by volume.

The discharge treatment can be carried out in the above-mentionedatmosphere gas by various discharging methods such as corona dischargeand glow discharge, and corona discharge is preferable from the pointthat a pressure inside an equipment is not required to be reduced, onlyone side of a film is easily treated when the molded article is a film,and an influence of the atmosphere gas around the electrodes is smalland thus stable discharging is easily obtained.

Discharging conditions may be optionally selected depending on desiredvalues of F/C and O/C, kind of the non-perfluoro fluorine-containingresin and kind and concentration of the reactive organic compound. Thedischarge treatment is carried out usually at a charge density in arange of 0.3 to 9.0 W·sec/cm², preferably less than 3.0 W·sec/cm². Atreating temperature can be optionally selected in a range of not lessthan 0° C. and not more than 100° C.

In the present invention, a part of the molded article is subjected todischarge treatment. Particularly in case where the molded article is inthe form of film or sheet, it is preferable that only one side of thefilm or sheet is subjected to discharge treatment and characteristics ofthe fluorine-containing resin is left on another side thereof.

For discharge treatment of one side of a fluorine-containing resin film,there is a method of corona discharging by using an earth electrode inthe form of roll and making the film contact with the earth electrode.However the method is not limited thereto.

The so-obtained discharge-treated molded article has a surface layerportion having a low temperature heat sealing property. The surfacelayer portion has a reduced F/C of 0.2≦F/C≦0.9 and O/C of 0.09≦O/C≦0.40.If F/C of the surface of discharge-treated molded article is less than0.2, a sufficient heat sealing strength cannot be obtained and in caseof a film, wrinkling arises due to heat generated at discharging, whichremarkably lowers product quality. If more than 0.9, a sufficient heatsealing strength cannot be obtained. On the other hand, if O/C is lessthan 0.09, a sufficient heat sealing strength cannot be obtained, and ifmore than 0.40, a sufficient heat sealing strength cannot be obtainedand in case of a film, wrinkling arises due to heat generated atdischarging, which remarkably lowers product quality. It is preferablethat the surface layer portion having a low temperature heat sealingproperty has F/C of 0.3≦F/C≦0.8 and 0/C of 0.14≦O/C≦0.3 from the pointthat a good adhesive strength can be obtained when films are heat-sealedwith each other at low temperature. It is further preferable that F/C is0.4≦F/C≦0.8 and O/C is 0.14≦O/C≦0.25 from the viewpoint of excellentdurability when the obtained laminated article is exposed to naturalenvironment. It is a matter of course that F/C of the surface layerportion having a low temperature heat sealing property is smaller thanF/C (0.7 to 1.8) of other (initial) surface layer portion.

In the present invention, the “surface layer portion” means a portion upto a measurable depth (about 10 nm) of the resin layer when measuringwith an X-ray photoelectron spectrometer (ESCA-750 available fromShimadzu Corporation) under the conditions of X-ray-energized Al, Kαl,2ray (1486.6 eV), X-ray output of 8 KV, 30 mA, temperature of 20° C. andvacuum degree of not more than 5.0×10⁻⁷ Torr. F/C and O/C are calculatedfrom C_(1s), F_(1s) and O_(1s), measured by that method.

The non-perfluoro fluorine-containing resin molded article of thepresent invention can be heat-sealed strongly enough with anothernon-perfluoro fluorine-containing resin molded article subjected todischarge treatment in the same manner or with other materials on thesurface layer portion having a low temperature heat sealing property. Anenough heat sealing strength means a strength where in case of rippingoff heat-sealed molded articles, the molded articles themselves arebroken. The strength can be evaluated by a tensile yield strength(gf/cm) in a tension test of each fluorine-containing resin moldedarticle (according to ASTM D 3368).

A tensile yield strength of a film varies depending on a thickness ofthe film. For example, in case of non-stretched ETFE film, a tensileyield strength of the film having a thickness of 6 μm which is thethinnest one available industrially is about 120 gf/cm. Therefore thefilm having at least such a tensile yield strength can be usedpractically. Further in case of 12 μm thick film which is used generallyin industries, it is preferable that a tensile yield strength is notless than about 240 gf/cm.

Also in case of adhesion to other material, for example, anethylene-vinyl acetate copolymer film which is used for a coveringlaminated film for solar batteries explained hereinafter, fromexperiential point of view, it is necessary that a surface thereofsubjected to discharge treatment has a heat sealing strength of not lessthan 360 gf/cm. In case of adhesion to other material of the same kind,a heat sealing strength higher than a strength at break of the materialof film itself is required. Also in case of a film like a coveringlaminated film for solar batteries which is subject to exposure tonatural environment such as irradiation of ultraviolet rays, permeationof steam and thermal shock, thus deteriorating an adhered surface, aheat sealing strength thereof does not depend on a strength of the filmitself, and a larger heat sealing strength is required.

Examples of other material which can be heat-sealed to the non-perfluorofluorine-containing resin molded article of the present invention are,for instance, synthetic resin materials such as ethylene-vinyl acetatecopolymer, polyimide and polyamideimide.

The heat sealing is carried out through known heat sealing method at atemperature of less than a melting point of the non-perfluorofluorine-containing resin, for example, in a temperature range of 140°C. up to the melting point thereof. Non-restricted examples of the heatsealing method are, for instance, an impulse heat sealing method, heatpress method, and the like.

The fluorine-containing resin molded article of the present inventionhaving a low temperature heat sealing property is useful for not only acovering film for solar batteries which is explained hereinafter butalso interior and exterior materials for building such as a decorativesteel plate and wall paper, covering material for electric wire, and thelike.

The present invention also relates to the covering film for solarbatteries comprising the non-perfluoro fluorine-containing resin filmsubjected to the above-mentioned discharge treatment. The covering filmis endowed with a low temperature heat sealing property only on one sidethereof, and other side remains un-treated to utilize characteristics ofthe fluorine-containing resin such as non-sticking property, waterrepellency, lubricity, stain-proofing property, chemical resistance andelectric insulation. The covering film for solar batteries of thepresent invention requires the above-mentioned heat sealing strength ofnot less than 360 gf/cm from the viewpoint of weather resistance anddurability.

The covering film for solar batteries of the present invention isusually in the form of a laminated article produced by heat-sealing atreated surface thereof to other material, for example, anethylene-vinyl acetate copolymer (EVA) film or sheet. The solar batteryis protected by that laminated article.

A thickness of the covering film for solar batteries is usually fromabout 50 μm to about 0.1 mm, and a thickness of EVA film or sheet isusually from about 0.1 mm to about 1.0 mm.

EXAMPLE

The present invention is then explained by means of examples, but is notlimited to them.

Example 1

One side of a 100 μm thick ETFE film (F/C=1.1, NEOFLON ETFE film EF-0100available from DAIKIN INDUSTRIES, LTD.) was subjected to coronadischarge treatment at a charge density shown in Table 1 by continuouslypassing the film along an earth electrode (60° C.) in the form of rollwhile flowing nitrogen gas containing 0.3 % by volume of vinyl acetateor glycidyl methacrylate in the neighborhood of a discharge electrodeand the earth electrode of a corona discharge equipment.

With respect to a surface layer portion subjected to corona dischargetreatment (having low temperature heat sealing property), F/C and O/Cwere calculated with the above-mentioned ESCA. The results are shown inTable 1.

Then two treated ETFE films were subjected to heat pressing at 170° C.for five minutes while the surface layer portions having low temperatureheat sealing property were faced with each other. Thus a sample formeasuring a heat sealing strength was produced. The sample was subjectedto 180° C. peeling test (drawing speed: 100 mm/min) in according to JISK 6845 by using a universal tensile tester (ASG-50D available fromShimadzu Corporation). Measured values are shown in Table 1 as a heatsealing strength.

TABLE 1 Surface layer portion Heat Charge having low temperature sealingdensity Reactive heat sealing property strength (W sec/cm²) organiccompound F/C O/C (gf/cm) 8.3 Vinyl acetate 0.1 0.42 132 0.8 Vinylacetate 0.8 0.17 539 0.4 Vinyl acetate 0.9 0.09 120 0.3 Vinyl acetate1.0 0.10  24 0.8 Glycidyl methacrylate 0.7 0.14 420 0.8 — 1.0 0.12  0

Example 2

ETFE films having a surface layer portion which has a low temperatureheat sealing property and various F/C and O/C values were produced inthe same manner as in Example 1 by optionally changing a concentrationof vinyl acetate and a charge density of corona discharging. A heatsealing strength thereof was measured in the same manner as in Example1.

The results are shown in FIG. 1. In FIG. 1, ◯ represents the film havinga heat sealing strength of not less than 360 gf/cm, □ represents thefilm having a heat sealing strength of not less than 240 gf/cm and lessthan 360 gf/cm, ▾ represents the film having a heat sealing strength ofnot less than 120 gf/cm and less than 240 gf/cm, ▾ represents the filmhaving a heat sealing strength of less than 120 gf/cm and x representsthe deformed film.

As shown in FIG. 1, if F/C exceeds 0.9, a heat sealing strength becomesless than 120 gf/cm and the film is easily peeled, and if F/C is lessthan 0.2, the film is deformed. Also if O/C exceeds 0.4, deformation ofthe film arises, and if O/C is less than 0.09, a heat sealing strengthlowers below 120 gf/cm. On the other hand, particularly in case whereF/C and O/C are 0.3≦F/C≦0.8 and 0.14≦O/C≦0.3, respectively, an excellentheat sealing strength can be obtained. Further in case where F/C and O/Care 0.4≦F/C≦0.8 and 0.14≦O/C≦0.25, respectively, a high heat sealingstrength required by a covering film for solar batteries can beobtained.

Example 3

ETFE films having a surface layer portion which have a low temperatureheat sealing property and F/C and O/C values shown in Table 2 wereproduced in the same manner as in Example 1 except that a 50 μm thickETFE film (F/C=1.1, NEOFLON ETFE film EF-0050 available from DAIKININDUSTRIES, LTD.) was used. Those ETFE films were heat-sealed with eachother in the same manner as in Example 1. A heat sealing strengththereof was as shown in Table 2.

On the surface of ETFE film having a low temperature heat sealingproperty were overlaid a EVA film (BOND FAST G available from SUMITOMOCHEMICAL INDUSTRY CO., LTD., 0.05 mm thick) and then an aluminum sheet(0.2 mm thick) subjected to greasing with acetone, followed by pressingat 60 gf/cm² and heating at 150° C. for two hours in an electric oven.Thus a laminated article was produced in imitation of a solar batterypanel. The obtained laminated article was allowed to stand inenvironment of a temperature of 85° C.±2° C. and a relative humidity of90 to 93±5% RH for 1,000 hours and taken out of the environment. Whetheror not there was a separation of the ETFE film and EVA film was checkedwith naked eyes. The results are shown in Table 2.

TABLE 2 Surface layer portion Heat Durability at high temperature havinglow temperature sealing and high humidity heat sealing property strength(85° C. ± 2° C., 90 to 93 ± 5 RH, F/C O/C (gf/cm) 1,000 hours) 0.4 0.26210 Peeling of ETFE film occurred. 0.5 0.26 340 Peeling of ETFE filmoccurred. 0.4 0.25 360 No change 0.7 0.14 870 No change

As shown in Table 2, in order to meet high weather resistance anddurability requirements as a cover film for solar batteries, a heatsealing strength of not less than 360 gf/cm is necessary.

INDUSTRIAL APPLICABILITY

According to the present invention, an excellent low temperature heatsealing property can be imparted to a non-perfluoro fluorine-containingresin which is difficult to heat-seal at low temperature, and also afluorine-containing resin film which can be used as a covering film forsolar batteries which is required to have high weather resistance anddurability can be provided.

What is claimed is:
 1. A non-perfluoro fluorine-containing resin moldedarticle having a surface layer; a part of the surface layer comprises asurface layer portion having a low temperature heat scaling property;said surface layer portion having a low temperature heat-sealingproperty has a ratio F/C of the number of fluorine atoms to the numberof carbon atoms of 0.2≦F/C≦0.9 and a ratio O/C of the number of oxygenatoms to the number of carbon atoms of 0.09≦O/C≦0.40, and a remainingpart of the surface layer has a ratio F/C of the number of fluorineatoms to the number of carbon atoms which is larger than that of thesurface layer portion having a low temperature heat-sealing property andis 0.8≦F/C≦1.8.
 2. The fluorine-containing resin molded article of claim1, wherein the ratio F/C of the number of fluorine atoms to the numberof carbon atoms of said surface layer portion having a low temperatureheat sealing property is 0.3≦F/C≦0.8 and the ratio O/C of the number ofoxygen atoms to the number of carbon atoms is 0.14≦O/C≦0.30.
 3. Thefluorine-containing resin molded article of claim 1, wherein the ratioF/C of the number of fluorine atoms to the number of carbon atoms ofsaid surface layer portion having a low temperature heat-sealingproperty is 0.4≦F/C≦0.8 and die ratio O/C of the number of oxygen atomsto the number of carbon atoms is 0.14≦O/C≦0.25.
 4. Thefluorine-containing resin molded article of claim 1, wherein a lowtemperature heat sealing property is exhibited at a temperature of notmore than a melting point of the non-perfluoro fluorine-containing resinmolded article.
 5. The fluorine-containing resin molded article of claim4, wherein said non-perfluoro fluorine-containing resin is anethylene/tetrafluoroethylene copolymer or polyvinylidene fluoride. 6.The fluorine-containing resin molded article of claim 1, wherein saidnon-perfluoro fluorine-containing resin molded article is a film.
 7. Acovering film for solar batteries which comprises the film of claim 6wherein a first side of said film has a surface layer portion having alow temperature heat sealing property and the surface layer of theopposite side of said film has a ratio F/C which is larger than that ofthe surface layer portion of said first side.
 8. The covering film forsolar batteries of claim 7, wherein the surface layer portion having alow temperature heat sealing property has a heat sealing strength of notless than 360 gf/cm.
 9. A covering laminated article for solarbatteries, which is produced by heat-sealing the covering film of claim7 directly with an ethylene/vinyl acetate film or sheet at a temperatureof less than a melting point of the non-perfluoro fluorine-containingresin.